The proposed research aims to address critical gaps in scientific knowledge of ozone and health with a national assessment of ozone and mortality and hospital admissions through epidemiological studies and biostatistical analysis. Specifically, the primary objectives are to investigate the relationship between ozone and mortality and hospital admissions, with respect to mortality displacement, longer-term exposure, the shape of the distributed lag curve, potential interaction with particulate matter (PM), heterogeneity among community-specific estimates, and threshold effects. Recent synthesis of scientific information on ozone and health by the United States EPA revealed considerable gaps in the literature on ozone and human health, including those outlined in the specific aims. This research directly relates to the NIEHS goals of reducing the burden of environmentally associated disease, contributing to career enhancement of young researchers, and providing a sound scientific foundation to support policy. More than 100 million people in the United States reside in areas exceeding the ozone standard, making ozone one of the nation's most pressing air pollution problems. A key component of the proposal is to investigate potential interaction between ozone and PM through the development of interaction models and through study of whether variation in PM composition can explain spatial and temporal heterogeneity in ozone effect estimates. This work is consistent with NIEHS initiatives to identify the health effects from complex mixtures and to develop statistical and mathematical models that accommodate complex mixtures. Results from this research are anticipated to be highly policy-relevant, both with respect to ozone and in the long-term with regards to air pollution and health more generally. An overall objective of this work is to contribute statistical techniques that could be applied broadly in environmental health research, such as to other health outcomes and other pollutants. Relevance to public health: This research investigates how hospital admissions and mortality are affected by ozone, a common urban air pollutant. The goal of this work is to provide policy-makers, scientists, and the public with a better understanding of how ozone affects health in order to aid more effective decisions regarding protection of human health.